The Bible--concerned with sanctity in all aspects of life--prohibits incest, adultery, and a number of other sexual relationships.

Although the technical term for sexual offenses in general is gillui arayot (literally, "the uncovering of nakedness"), the term is usually employed to denote carnal knowledge and unethical sex.
In the present context, however, sexual offenses include offenses committed by prohibited sexual intercourse, offenses of unlawful sexual conduct short of intercourse, and related offenses presumably motivated by the sexual urge.

Following is the famous biblical passage from chapter 18 of the Book of Leviticus, which was chosen as the Torah reading for the afternoon of Yom Kippur, the Day of Atonement. The passage condemns adultery and other immoralities. Following the announcement of forgiveness by the High Priest, at the conclusion of the Avodah service in the Temple, the maidens danced in the vineyards and betrothals were announced. The Torah reading of Leviticus 18 was likely selected for Yom Kippur afternoon to impress upon the young people the need to maintain Israel's high standard of family morality. Impurity in marriage, incestuous promiscuity among near relations, and other abominations were condemned and regarded as grave sins.

The retention of this biblical passage was likely prompted by the desire to inculcate on the Day of Atonement the paramount duties of self‑control and connubial purity, which have proved such potent factors in the survival of the Jewish people. To be reconciled with God and with our fellow human beings, we must be chaste in body, wholesome in mind, and pure in heart. A high standard of domestic fidelity is the basis of a happy home and a moral home is the foundation of an enduring civilization.

Here is the passage from Leviticus 18:

"…None of you shall approach to any that is near of kin to him, to uncover their nakedness, I am the Lord. The nakedness of your father, even the nakedness of your mother, shall you not uncover. She is your mother, and you shall not uncover her nakedness. The nakedness of your father's wife shall you not uncover; it is your father's nakedness. The nakedness of your sister, the daughter of your father, or daughter of your mother, whether she be born at home, or abroad, even their nakedness you shall not uncover. The nakedness of your son's daughter, or of your daughter's daughter, even their nakedness you shall not uncover. For theirs is your own nakedness. The nakedness of your father's wife's daughter, begotten of your father, she is your sister, you shall not uncover her nakedness. You shall not uncover the nakedness of your father's sister; she is your father's near kinswoman. You shall not uncover the nakedness of your mother's sister, for she is your mother's near kinswoman. You shall not uncover the nakedness of your father's brother, you shall not approach his wife. She is your aunt. You shall not uncover the nakedness of your daughter‑in‑law; she is your son's wife. You shall not uncover her nakedness. You shall not uncover the nakedness of your brother's wife; it is your brother's nakedness. You shall not uncover the nakedness of a woman and her daughter; you shall not take her son's daughter, or her daughter's daughter, to uncover her nakedness; they are near kinswomen; it is lewdness. And you shall not take a woman to her sister, to be a rival to her, to uncover her nakedness, besides the other in her lifetime. And unto a woman separated by her menstrual impurity you shall not approach to uncover her nakedness. And you shall not lie carnally with your neighbor's wife, to defile yourself with her. And you shall not give any of your seed to set them apart for Molech [a god worshipped through child sacrifice], neither shall you profane the name of your God. I am the Lord. You shall not lie with mankind as with womankind. It is an abomination. And you shall not lie with any beast to defile yourself therewith; neither shall any woman stand before a beast, to lie down thereto; it is perversion. Defile not yourselves in any of these things, for in all these, the nations are defiled, which I cast out before you (Leviticus 18:6-24)."